Over the next five years neuroimaging studies will explore the involvement of important neurotransmitter systems including the acetylcholine (ACH), dopamine (DA), and glutaminergic (GLU) system. We will extend our recent findings of a relationship between aspects of clinical severity and reduction in vesicular transport measured by IBVM to children (sibling and Down syndrome controls). We will introduce the study of the .alpha4/beta2 nicotinic receptor as a component of the ACH system with novel imaging studies involving selective ligands (5-1A and 2-FA) in comparison of RS with similar control groups (Aim 1a). Our studies of in vivo GLU function are developed to answer two questions: 1) GLU activity as a function of age studied by magnetic resonance spectroscopy (MRS) from childhood to adult; and 2) GLU abnormalities measuring potential of the NM DA glutamate system to enhance DA release using an amphetamine/ketamine challenge (adult RS and normal controls). These two measures complement each other and expand upon postmortem studies of NMDA glutamate by Lu and Johnson. This new PET approach, documented in controls, will: 1)prove a more optimal measure of GLU control of DA release, 2) correlate clinical features, and 3) determine a rationale for treatment with dextromathorphan (Dr. Naidu's project). Novel studies of the MeCP2 gene in mouse, DA receptors/transporters, and nicotinic cholinergic receptors will be conducted using this newly acquired mouse PET and mouse SPECT capability, allowing for manipulations such as mouse cholinergic studies including donepril. Thus, we expect to have the definitive story concerning the role of the acetylcholine system in adult and childhood RS, to characterize the glutamate NMDA system from childhood to adult RS, and to set the stage for treatments such as dextromathorphan and other non-competitive NMDA inhibitors as the acetylcholine studies will inform us of potential cholinergic agents that affect cognition including nicotinic and acetylcholinesterase inhibitors. Finally our PET and SPECT studies of the relationship between mutations both for mouse and human studies expand our view of these neurotransmitter systems and treatment implications in the pathophysiology of RS and complement the MRI/MRS studies in Project 1.